The present invention relates to lasers, and more particularly to an upconversion laser which can provide red, green and blue light from a single wavelength pump infrared laser.
In a conventional solid state laser, optical pumping is used to achieve a population inversion. Absorption of pump photons populates an excited state of the active ion which in general lies above the initial laser level.
Upconversion mechanisms that convert infrared radiation to visible radiation have been known for many years in the field of phosphors. Recent reports of laser pumped laser operation have also appeared based on these processes. See, e.g. "Ion-pair upconversion laser emission of Er.sup.3+ ions in YAG, YLF.sub.4, SrF.sub.2 and CaF.sub.2 crystals," S. A. Pollack and D. B. Chang, J. Appl. Phys., Vol. 64, page 2885 (1988); and "An infrared pumped erbium upconversion laser," A. J. Silversmith, W. Lenth, and R. M. MacFarlane, Appl. Phys. Lett., Vol. 51, page 1977 (1987). Using infrared pumping, laser emission has been obtained in the green, red and infrared. Laser operation at shorter wavelengths has required either a single yellow pump or a combination of IR and either yellow or red for all lasers operating at a wavelength shorter than 550 nm.
Energy addition using two pump wavelength excitation has been reported for UV/violet/blue laser output. LaF.sub.3 :Nd.sup.3+ pumped simultaneously at 591 nm and 788 nm has produced 380 nm laser output. "Violet CW neodymium upconversion laser," R. M. Macfarlane, F. Tong, A. J. Silversmith and W. Lenth, Appl.Phys. Lett., Vol. 52, page 1300 (1988). YLiF.sub.4 :Tm.sup.3+ pumped at 649 nm and 781 nm has produced a pulsed output at 450 nm. "Blue-green (450 nm) upconversion Tm.sup.3+ :YLF laser," D. C. Nguyen, G. E. Faulkner and M. Dullick, Appl. Optics, Vol. 28, page 3553 (1989). The yellow wavelengths are not available from semiconductor diode sources, though the 780 pump wavelengths are.
Single pump experiments have produced 551 nm laser action in YLiF.sub.4 :Er.sup.3+ for 820 nm excitation. "An Infrared pumped erbium upconversion laser," id. Laser operation at 413, 730 and 1053 nm has been reported for YLiF.sub.4 :Nd.sup.3+ pumped at 604 nm. "Laser emission at 413 and 730 nm in upconversion-pumped YLiF.sub.4 :Nd.sup.3+," F. Tong, R. M. Macfarlane and W. Lenth, Technical Digest of Conference on Quantum Electronics and Laser Science (Optical Society of America, Washington DC 1989), Paper THKK4. For CW excitation in the vicinity of 800 nm, obtainable from semiconductor diodes, only one visible output wavelength, 551 nm, is known to have been reported by other workers.
The kinetics involved in the upconversion process involving rare earth ions are very complex and remain to be completely characterized.
Red-green-blue multicolored displays using efficient small size sources are needed for simulation purposes in training systems and for automotive and/or aircraft displays of all kinds. The improved efficiency of semiconductor laser pumped systems and the small size that they can achieve would greatly expand the number of application areas.